In a hypertorus model of the Universe, motion in a straight line will return you to your original location, even in an uncurved (flat) spacetime. The Universe could also be closed and positively curved: like a hypersphere. (ESO AND DEVIANTART USER INTHESTARLIGHTGARDEN)

Three of our dimensions are spatial and one is temporal, but could there be more?

From any point in space, you are free to move in any direction you choose. No matter how you orient yourself, you can travel forwards-or-backwards, up-and-down, or side-to-side: you have three independent dimensions that you can navigate. There is a fourth dimension: time; we move through that just as inevitably as we move through space, and via the rules of Einstein’s relativity, our motion through space and time are inextricable from one another. But could additional motions be possible? Could there be additional spatial dimensions beyond the three that we know? …


Chinese virologist Shi Zhengli (L) is seen inside the P4 laboratory in Wuhan in this 2017 photo. The P4 epidemiological laboratory, part of the Wuhan Institute of Virology, is one of the world’s leading research centers on coronaviruses. (Johannes Eisele / AFP via Getty Images)

Despite the enormous flood of recent reports, there’s no good evidence for a lab leak.

At the very end of 2019, a new disease began to emerge in humans: COVID-19. Originally described as a set of pneumonia-like symptoms with a hitherto unseen cause, a set of alarming facts soon came to light. A novel virus — now known to be SARS-CoV-2 — had begun infecting humans, with the first major outbreak stemming from a wet market in Wuhan: the largest city by far in the Chinese province of Hubei. The next pandemic, just as virologists and disease ecologists had been predicting for years, emerged from the continued encroachment of human civilization on territory previously inhabited…


The Dark Energy Survey’s CCD plane (L) and field-of-view (R). With six years of data under its belt and the year three data release and analysis just having been completed, it’s a fascinating chance to compare these new observations with our best cosmic theories and the data from other sources. (CTIO/FERMILAB/DES COLLABORATION)

With 5,000 square degrees of data, the Dark Energy Survey has something important to say.

For as long as humans have been studying the Universe, we’ve yearned to know the answers to the biggest questions of all. What, exactly, is out there in the abyss of deep space? Where did it all come from? What is it made out of, and how did it get to be this way? And, moreover, what will its ultimate fate be? …


This X-ray/radio panorama of the galactic center takes data from NASA’s Chandra and South Africa’s MeerKAT telescopes. X-rays from Chandra are orange, green, and purple, showing different X-ray energies, and the radio data from MeerKAT are gray. A variety of interconnected features are on display here, enabling us to uncover the origin of galactic energy transport. (X-RAY: NASA/CXC/UMASS/Q.D. WANG; RADIO: NRF/SARAO/MEERKAT)

With radio and X-ray data combined, we’re understanding how energy flows like never before.

When we look out at the Universe on the largest cosmic scales of all, gravity is the only force that matters. Even though the other fundamental forces of nature are far stronger, the weak and strong nuclear forces are only short-range forces, while the Universe is electrically neutral overall, leaving gravitation alone to dominate. But inside large, massive structures like galaxies, the normal matter contracts and collapses, forming stars and gas clouds, interacting with black holes and neutron stars, and experiencing otherwise “messy” physical conditions.

In our nearby Universe, no place is messier than our galactic center. Located some 27,000…


Michael Collins, Apollo 11 crewmember and ‘loneliest human’ ever, with lunar tribute. Collins died in April of 2021, surviving more than 50 years since the historic Apollo 11 Moon landing, for which he was in orbit around the Moon. The image of the Moon is made entirely of the Apollo 11 transcript, an incredibly artistic touch to the astro compositions of J-P Metsavainio. (J-P METSAVAINIO (L); ERIC BARADAT/AFP VIA GETTY IMAGES (R))

The sacrifices of early astronauts paved the way for Apollo’s successes, and so much more.

In all of history, only 24 humans have ever escaped Earth’s gravity.


(Image credit: V. Belokurov and A. Smith; acknowledgement: Markus and Gail Davies; Robert Gendler)

Our galaxy not only isn’t stationary, but different parts are accelerating at different rates.

When we think about the Universe as a whole, the accelerations that objects experience from our perspective are overwhelmingly due to the expansion of the Universe. Nearby, however, it’s the local gravitational effects of nearby masses that dominate. Within our own Local Group, we’ve been able to discover that the Milky Way is not some quiet, massive spiral just going about its own business, but rather that it’s being tugged in a variety of ways from the large masses around it, including a nearby galaxy that was only discovered in very recent years: Antlia 2.

This is one of the…


An illustration of multiple, independent Universes, causally disconnected from one another in an ever-expanding cosmic ocean, is one depiction of the Multiverse idea. The idea that two of these bubble Universes could have collided or otherwise interacted is disfavored by both theory and observation. (OZYTIVE / PUBLIC DOMAIN)

It’s a wild idea, but there’s a way to test it.

No matter how far we look out in the Universe, there’s always more “Universe” to see. Even at the extreme limits of what’s visible — 46 billion light-years in all directions, given the finite amount of time that’s passed since the Big Bang, the expanding Universe, and the finite speed of light — there’s no evidence of all sorts of weirdness we’ve imagined. There’s no edge to the Universe, no departures from large-scale uniformity, no evidence for a preferred direction, and no evidence of repeating patterns. Even so, it’s important to keep our minds open to all the possibilities that…


A distant, background galaxy is lensed so severely by the intervening, galaxy-filled cluster, that three independent images of the background galaxy, with significantly different light-travel times, can all be seen. In theory, a gravitational lens can reveal galaxies that are many times fainter than what could ever be seen without such a lens. (NASA & ESA)

And a combination of all three might take us farther than ever.

If you want to see the farthest objects in the Universe, you have to know not only where to look, but how to optimize your search. Historically, the larger our telescopes got, the more light they could gather, and hence the fainter and more distant they could look out into the Universe. When we added photography into the mix — or the ability to capture large amounts of data over long periods of time — we could both see greater amounts of detail and reveal objects that were farther away than ever before.

But still, that approach itself had fundamental…


An artist’s rendition of the approved and selected LightCube CubeSat mission. When activated, an optical flash will be emitted, creating the brightest artificial point source ever made by humanity in space. (ARIZONA STATE UNIVERSITY / NASA)

‘Fast Optical Bursts’ will confound ground-based astronomy.

As of 2021, planet Earth is currently experiencing the least pristine night sky in recorded history. Prior to the development of artificial lighting, the naked human eye could see up to 6,000 stars on a clear, moonless night. Today, there are only a few locations left on Earth’s land masses — mostly isolated in a few Dark Sky preserves or where professional observatories are located — where light pollution from the ground doesn’t severely reduce what the human eye can see. …


The fabric of expanding space as illustrated over cosmic time. One of the consequences of the expansion is that the farther away a galaxy is, the faster it appears to recede from us, and that the farther away a light source is, the greater the redshift of the light’s wavelength by the time we receive it. (NASA, GODDARD SPACE FLIGHT CENTER)

Or is ‘new space’ created in between the gaps of the ‘old’ space?

It’s been almost 100 years since humanity first reached a revolutionary conclusion about our Universe: space itself doesn’t remain static, but rather evolves with time. One of the most unsettling predictions of Einstein’s General Relativity is that any Universe — so long as it’s evenly filled with one or more type of energy — cannot remain unchanging over time. Instead, it must either expand or contract, something initially derived independently by three separate people: Alexander Friedmann (1922), Georges Lemaitre (1927), Howard Robertson (1929), and then generalized by Arthur Walker (1936).

Concurrently, observations began to show that the spirals and ellipticals…

Ethan Siegel

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.

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